A suctioning counter-pressure casting method has been proposed which can be used to cast thin products with reduced heating of molten metal at reduced mold temperature (see JP 2933255B2).
In the suctioning counter-pressure casting method, the lower part of a stalk is dipped in molten metal that is held in the lower part of a pressure-bearable hermetic holding furnace, a horizontally openable mold communicating with the stalk is placed above the stalk in a vertically movable manner, and a hermetic chamber covering the mold is formed. Then, a suction on-off valve in a communication pipe communicated with the hermetic chamber is opened so that the pressure in the hermetic chamber is reduced to 100 Torr within 1 second by mean of a vacuum pump through a vacuum tank. Then, a pressure on-off valve is immediately opened, and compressed air is pumped into the holding furnace by means of a compressor, so that the pressure on the surface of the molten metal is increased to 0.4 to 1 kg/cm2 within 1 second and is maintained at the increased level. When a casting is solidified, the reduced pressure and the maintained increased pressure are released.
However, in the suctioning counter-pressure casting method of JP 2933255B2, the air in the cavity is indirectly suctioned by decompression of the outside thereof. Accordingly, the degree of decompression and the decompression rate depend on the clearance between the mold faces of the split mold, the cavity volume and the volume of the hermetic chamber that surrounds the split mold to cover the entire split mold.
Therefore, for example, a problem in the production of a molded product with such a complex shape that requires the use of a split mold and a core is that only such indirect suction of the air in the cavity by decompression of the outside thereof is not enough to stabilize the degree of decompression and the decompression rate of the cavity within a suitable range, which may result in the degraded filling performance of molten metal.
Another problem with the casting device of JP 2933255B2 is high facility cost due to the hermetical chamber that covers the entire mold.